Touch panels are electronic components that function as location input devices, and are used in a wide range of applications such as cell phones or portable game devices by combining with a display device in the manner of a liquid crystal panel. A touch panel is an interface capable of performing a suitable operation desired by an operator by sensing information relating to a specific location when the operator points to that specific location on the touch panel with a finger or input pen based on a screen display.
Although touch panels employ methods based on various principles to detect a pointed location, a detection method employing a resistive film has been widely used thus far. The resistive film detection method involves detecting a location based on a voltage between two opposing transparent, conductive films. When a voltage is applied to one of the two films, a voltage corresponding to a location of the transparent conductive film that has been operated is generated in the other transparent conductive film. The location that has been operated can be specified by detecting that voltage.
On the other hand, in addition to touch panels being highly accurate, highly durable and highly sensitive, following the development of multi-touch systems in recent years, the use of electrostatic capacitive touch panels has rapidly proliferated primarily in mobile devices such as cell phones. With the growth of devices in which these touch panels are installed and the environment in which they are used, along with increasing diversification of the types of these touch panels that are available, these touch panels are expected to surpass the number of resistive film types in the future.
Two examples of typical detection methods employed by electrostatic capacitive touch panels include analog detection surface types and projective types employing an integrating detection system using patterned electrodes. Moreover, although numerous proposals have been made for each system and manufacturer for the configuration of projective types, many projective types that have recently demonstrated a sudden increase in popularity impart durability by using a glass or resin plate for the protective plate of the insulating layer interposed between conductive layers or the surface. In the future, the use of various types of resin film films for these components is expected to result in a growing trend towards reduced costs and increased flexibility.
Since the conductive layer serving as a critical component of touch panels is intended to demonstrate both conductive performance and transparency, an ITO (indium tin oxide) layer formed by a dry method such as sputtering or vapor deposition is used most commonly.
However, since dry ITO layers are comparatively brittle and have low shock resistance due to their production method and components, there is the risk of damage due to impacts resulting from dropping and the like. Moreover, since they are also susceptible to bending, when a film is used to make the structural materials of a touch panel flexible, there is the risk of considerable decrease in durability. Therefore, studies have been conducted on the use of a conductive layer formed by a wet method that is capable of improving shock resistance and bendability.
Although there are various types of materials used for conductive layers capable of being formed by a wet method, including metal oxide-based materials such as ITO or ATO, metal-based materials such as silver or copper, and conductive carbon nanofibers, if the emphasis is placed on bendability, then organic conductive polymers are preferable.
In particular, numerous studies are being conducted on polythiophene-based since they are capable of realizing both electrical conductivity and transparency. However, since these polymers are prepared in the form of an aqueous dispersion, there are concerns over wetting following deposition as well as decreases in quality when used in high-humidity environments. Therefore, Patent Document 1 proposes the formation of a protective layer by thermal bonding a transparent insulating sheet to a conductive layer composed of a conductive polymer.
In addition, in the case of touch panels, there are many cases in which conductive layers are used as members by laminating with an adhesive, and in the case of projective-type, electrostatic capacitive touch panels in particular, this configuration is employed over nearly the entire display screen.
However, in the case of dry ITO layers that were used most commonly in the past, since corrosion of the conductive layer leads to inferior quality when combined with an adhesive containing an acidic component, countermeasures have been proposed and used in finished products consisting of, for example, using an adhesive that does not contain an acidic component as is proposed in Patent Document 2.